Oxide piezoelectric material

ABSTRACT

AN OXIDE PIEZEOLECTRIC MATERIAL ESSENTIALLY CONSISTING OF 50.0 TO 1.0 MOL PERCENT OF PB(CD1/3-$NB2/3)O3, 34.0 TO 55.5 MOL PERCENT OF PBTIO3 AND 16.0 TO 53.3 MOL PERCENT OF PBZRO3 ASSUMING THE FORM OF SOLID SOLUTION. THE MATERIAL MAY FURTHER CONTAIN AT LEAST ONE OF MNO2, CR2O3, NIO, COO, LA2O3, BI2O3, THO2 AND CEO2.

May 9, 1972 NOBORU lcHlNosE ErAL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL 17 Sheets-Sheet 1 Filed Feb. 24, 1970 Pb(Cd1/3Nb2,3)03

O {OO o 400 PbZrOEs zooo 6b PbTlos mov/ 31 Pbzros(mo\%) FIGZ Qav. PzmEmmOo wZDaDOO 440.24105 -Omkoml FIG.

May 9, 1972 NoBoRU lcHlNosE ET AL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL Filed Feb. 24, 1970 1v sheets-sheet a FIG. 3

|- '2000 g z u.. 70 O E o 60 ro 50 E 40 |000 :l 5 J o 30 .J z 5 20 i0- o o o 5 so 5| Pb(Cd v3Nb2/3)O3(mol "J 5o 42 34 Pbioawon 50 33 46 PbZr03(mol%) DIELECTRIC CONSTANT -ioo 16o 26o .36o 40o TEMPERATURE (c) FIGA May 9, 1972 NoBoRu lcHlNosE EVAL 3,661,781

OXIDE FIEZOELECTRIC MATERIAL 17 Sheets-Sheet 5 Filed Feb. 24, 1970 FIG. 5

10o zo 36o TEMPERATURE (c) IOO- i000 TIME AFTER POLARlZATION (Hr) iOOOO May 9, 1972 NoBoRu lcHlNosE ETAL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL Filed Feb. 24, 1970 17 Sheets-Sheet 4 FIG.

1600 TIME AFTER PoLARlzATloN (Hr) FIG.

O 6 @Lax .rZm-Omwoo @235C 75 PbTioa(mo| 17 PbZrO3(mol May 9, 1972 NoBoRU lcHlNosE ETAi OXIDE FIEZOELECTRIC MATERIAL 17 Sheets-Sheet 5 Filed Feb. 24, 1970 FIG.

IOOO

FIG.|G

46 Pbzros(mo| TEMPERATURE (C) w .53.5200 O POmI-m May 9, 1972 Filed Feb. 24, 1970 ELECTRO-MECHANICAL COUPLING COEFFICIENT KP(%) mcREAsE IN REsoNANoE FREQUENCY(%) NOBORU ICHINOSE ETA- OXIDE PIEZOELECTRIC MATERIAL l? Shees-Sheet 5 FIG. Il

50 200 2500 TEMPERATURE (c) FIG. 12

100 1000 iofooo TIME AFTER POLARIZATION (Hr) May 9, 1972 NoBoRu lcHlNosE ET AL 3,661,781

OKIDIS PIEZOELECTRIC MATERIAL 17 Sheets-Sheet 7 Filed Feb. 24, 1970 O m O iOOOO 1 OOO PbTiO3(mol%) 16o TIME AFTER PoLAR|zAT|oN(Hr) l: G. I4

o 2 4. e. .o o o .6 m 5 gni zmrimoo wznoo e m m o May 9, 1972 NOBORU lcHlNosE ET AL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL Filed Feb. 24, 1970 l? Shees-Sheet 8 FIG. I LZOOO FIG. I6

DlELECTRlC CONSTANT E 10o zo 50o 40o TEMPERATURE (C) May 9, 1972 NoBoRu lcHlNosr-g ETAL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL 17 Sheets-Sheet Filed Feb. 24, 1970 FIG,

FIG. 18

.Il M Mm 1 0 [md 2\/ Lm 4 w H M m m. O P R 0E mW W n m O. O. O. Q

May 9, 1972 NoBoRU lcHlNosE ETAL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL Filed Feb. 24, 1970 17 sheets-sheet 1o DECREASE lN ELECTRO-MECHANICAL COUPLING COEFFICIENT KP(%) 16o 1.600 10.000 TIME AFTER PoLARlZATloN (Hr) VAR|AT|0N IN REsoNANcE FREQUENCY -o -2'0 2o 4o eo eo TEMPERATURE (C FIGB?) May 9, 1972 NOBORU lcHlNosE ET AL 3,661,781

oxIDE PIEZOELECTRIC MATERIAL Filed Feb. 24, 1970 17 Sheets-Sheet 11 WO HOLOVd lVlVnO 'WOINVHOBW (mol FIG. 2O

5o Pbd MSNM/3) os mo| 34 PbTiOs i6 PbZrOS IDN May 9 1972 NoBoRU lcHlNosE ET AL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL 17 Sheets-Sheet 12 Filed Feb. 24, 1970 m m U m R F. D. M O E mw T l... o 2 2 2 x w 5,528 9505MB May 9, 1972 NOBORU ICHINOSE ETAL OXIDE PIEZOELECTRIC MATERIAL 17 Sheets-Sheet 1 3 Filed Feb. 24, 1970 FIG. 23

map24 TIME AFTER POLARIZATION (Hr) May 9, 1972 NoBoRu lcHlNosE ErAL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL Filed Feb. 24, 1970 17 sheets-sheet 14 DECREASE IN ELECTRO-MECHANCAL COUPLING COEFFICIENT KP(/o) "L 100 ipoo TIME AFTER PoLARlzATloN (Hr) FIG.25

FIG.26

TEMPERATURE C) OXIDH PIEZOELECTRIC MATERIAL 17 Sheets-Sheet 15 Fil-ed Feb. 'f2/1, 1970 FIG 27 O O O FIG. 28

3o Pbzroshnm May 9, 1972 NoBoRu lcHlNosE ETAL 3,661,781

OXIDE YIEZOELECTRIC MATERIAL 17 Sheets-Sheet 16 Filed Feb. 24, 1970 FI G l OO TEMPERATLRE (C) 2OOFIGQO K 10o TEMPERATURE (c) 0 O O m O May 9, 1972 NoBoRu lcHlNosE ETAL 3,661,781

OXIDE PIEZOELECTRIC MATERIAL Filed Feb. 24, 1970 17 Sheets-Sheet 17 FIG. 31

s 5 0.20 Z LLI LLI E 0.15 of Lu O ,12,3 g 0.10 LIJ [I g 397 u.: 0.05 (D 1 LLI C! O l TIME AFTER POLARIZATION (Hr) DECREASE IN ELECTRO-MECHANICAL COUPLING COEFICIENT KP("/o) TIME AFTER POLARIzAnoN (Hr) Patented May 9, 1972 3,661,781 OXIDE PIEZOELECTRIC MATERIAL Noboru Ichinose, Yokohama-shi, Harutoshi Egamr, Tokyo, and Katsunori Yokoyama and Yoshikazu Tanno, Yokohama-shi, Japan, assignors to Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan Filed Feb. 24, 1970, Ser. No. 13,741 Claims priority, application Japan, Feb. 24, 1969, 44/13,164; July 22, 1969, 44/57,424; Aug. 11, 1969, I4/62,902; Oct. 14, 1969, 44/81,526; Nov. 26, 1969, 44/94,250

Int. CI. C04b 35/46, 35/48 U.S. Cl. 252-629 6 Claims ABSTRACT oF THE DISCLOSURE An oxide piezeolectn'c material essentially consisting of 50.0 to 1.0 mol percent of Pb(Cd1/3Nb2/3)O3, 34.0 to 55.5 mol percent of PbTiO3 and 16.0 to.53.3 mol percent of PbZrO3 assuming the form of solid solution. The material may further contain at least one of MnOg, (21.203, COO, 143203, Bizog, and C602.

The present invention relates to an oxide piezoelectric material and particularly to an oxide piezoelectric material essentially consisting of a solid solution involving Pb(Cd1/3Nb2/3)O3, and PbZO'g synthesized solid phase reaction from various kinds of oxides.

As is well known, piezolectric materials are widely used as a transducer, for example, an oscillation element for generating supersonic waves or an element involved in a mechanical filter, ceramic lter, pickup, microphone and oscillograph and also as an ignition plug for gas implements and lighters. For such application there have already been provided oxide piezoelectric materials of the so-called Pb (Ti-Z003 system prepared into the form of solid solution consisting of, for example, equal mols of PbTiO3 and PbZrO3. Piezoelectric materials ofthe aforesaid system indeed have more excellent piezoelectric properties than those like BaTiO3, but have the drawbacks that they generally display unsatisfactory sintering properties, a small mechanical quality factor QM and a relatively small electro-mechanical coupling coetiicient, failing fully to meet practical requirements.

Recently, there have been made advanced studies in improving the piezoelectric materials of the Pb (Ti-Zr)03 system, as disclosed in a great deal of literature and numerous patents. The proposed methods for improving said piezoelectric properties may be broadly classified into the following two categories:

(l) Incorporation of additives in the basic constituent of a piezoelectric material,

(2) Addition of a third component to two components forming said basic constituent to prepare a ternary product.

While these approaches are gradually improving the piezoelectric properties, they are still unsatisfactory as exemplified below:

(a) Referring to the process (1) above of incorporating additives, there is known a method of adding CdO or ZnO to the basic constituent as disclosed in the British Pat. 953,408. Even with a piezoelectric material whose properties are improved by this method, the electromechanical coupling coeiiicient Kp stands at 37 to 48%, namely, does not attain 50%.

(b) With respect to the process (2) above of adding a third componentythere is proposed a ternary product consisting of PbTiOS and PbZrO3 as basic components and Pb(Mg1/3-Nb2/3) as a third component (Journal of American Ceramic Society, vol. 48, No. l2, pp. S30-635, 1965). With this process, Kp does not account for 50% and QM falls below 600. To give an extreme case, Kp only indicates 7.5% when QM stands at 568.

With oxide piezoelectric materials, it is generally demanded that both Kp and QM be as large as possible. Where there is prepared a piezoelectric material as an element for electro-mechanical conversion of oscillations in a mechanical lilter or as an element for electro-acoustic conversion of oscillations in a powerful supersonic wave oscillator, a large value of Kp improves the eiciency of conversion, oiering many advantages from the standpoint of circuit arrangement. Further, where there is to be conducted an electro-mechanical acoutic conversion, al

large value of QM reduces loss occurring in an oscillation element and in consequence unnecessary energy loss. This is the reason why the piezoelectric material is required to have a large value of both Kp and QM. The good properties of a piezoelectric element assumes great importance when it is employed in numerous applications, particularly electrical communication where there is being made prominent technical progress. Accordingly, there is great demand for development of a piezoelectric material having excellent properties.

The object of the present invention is to provide an oxide piezoelectric material which indicates high stable values of both electro-mechanical coupling coeiiicient and mechanical quality yfactor regardless of temperature change and over a long period of time.

The present invention provides an oxide piezoelectric material essentially consisting of a solid solution represented by the following formula:

x=50.0 to 1.0 mol percent y=34.0 to 55.5 mol percent z=l6.0 to 53.5 mol percent For improvement of its properties, this piezoelectric material may contain an auxiliary component such as M1102, CI'203, COO, 1.43203, Bl203, 17h02 Or C602. These auxiliary oxide components may be added to said solid solution or basic constitutent alone or in combination as NiO and CoO, La203 and Bi203, or ThO2 and C602.

It has been found that the oxide piezoelectric material of the present invention, with or without such auxiliary component, has a noticeable advantage that it displays prominently higher values of both electro-mechanical coupling coeicient and mechanical quality factor then those previously known and that these properties remain very stable regardless of temperature change and over a. long period of time. When determined for variations in the resonance frequency over a temperature range of -40 to 80 C., a resonator prepared from the oxide piezoelectric material of the present invention showed variations of i0.1% at most, whereas that of the prior art material varied as much as about l0.3%. Further when examined for qualitative deterioration during a period of 1,000 hours after polarization, the resonator of the present invention indicated variations of 10.1% at most as against 0.4% observed in that of the prior art. (Variations in the resonance frequency over a temperature range of 40 to 80 C. are presented in Examples 1V and VV.)

This invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1 is a triangular diagram showing the lrange of composition of a ternary oxide system forming the basic constituent of an oxide piezoelectric material according to the present invention;

FIG. 2 is a curve diagram of piezoelectric properties where the proportions of PbTiO3 and PbZrO3 are varied with those of Pb(Cd1/3Nb2/3)O3 and MnO2 fixed;

FIG. 3 is a curve diagram of piezoelectric properties where the proportions of Pb(Cd1/3Nb2/3)O3, PbTiOsand PbZrO3 constituting the ternary oxide system of the basic constitutent are varied with that of auxiliary Mn02 unchanged;

AFIGS. 4 and 5 are curve diagrams showing the relationship of the dielectric constant and electro-mechanical coupling coeilicient with respect to temperature variation as associated with two samples of the present invention containing Mn02 as an auxiliary component;

- FIGS. I6 and 7 are curve diagrams showing increase in the resonance frequency and decrease in the electromechanical coupling coeiiicient after polarization as associated with other samples of the invention similarly containing MnOZ as an auxiliary component;

FIG. 8 is a curve diagram showing piezoelectric properties where the proportions of PbTiOa and PbZrO3 are varied with those of Pb(Cd1/8Nb2/3)O3 and auxiliary MnOz unchanged;

FIG. 9 is a curve diagram showing piezoelectric properties where the proportions of Pb(Cd1/3Nb2/3)O3, PbTi03 and PbZrO3 are varied with that of auxiliary Cr203 unchanged;

FIGS. 10 and 11 show the piezoelectric properties of two samples of the invention containing auxiliary Cr203; FIG. 10 is a curve diagram of the relationship of temperature and dielectric constant and FIG. 11 is a curve diagram of the relationship of temperature and electromechanical coupling coeicient;

FIGS. 12 and 13 comparatively indicate the properties after polarization of two samples of the invention only consisting of the basic constituent and two other samples containing auxiliary CrgOa; FIG. 12 is a curve diagram of change with time in the resonance frequency andk FIG. 13 is a curve diagram of change with time in the electro-mechanical coupling coefficient;

FIG. 14 is a curve diagram of piezoelectric properties where the proportions of PbTiO3 and PbZrO3 are varied with those of Pb (Cd1/3Nb2/3)03 and auxiliary NiO iixed;

FIG. 15 is a curve diagram of piezoelectric properties where the proportions of Pb(Cd1/3Nb2/3)O3, PbTiO3 and PbZrO3 are varied with that of auxiliary CoOfixed;

' FIGS. 16 and 17 show the properties of oxide piezoelectric materials containing NiO and C00 respectively as an auxiliary component; FIG. 1-6 is a curve diagram of the relationship of temperature and dielectric constant and FIG. 17 is a curve diagram of the relationship of temperature and electro-mechanical coupling coefficient;

FIGS. 18 and 19 show the properties after polarization of two samples of the invention consisting of the basic constituent and two other samples containing auxiliary C00; FIG. 18 is a curve diagram showing change with time in the resonance frequency and FIG. 19 `is a curve diagram showing change with time in the electro-mechanical coupling coefficient;

FIG. 20 is a curve diagram of piezoelectric properties where the proportions of Pb(Cd1/3Nb2/3)O3, PbTiO3 and PbZrO3 are varied with that of Bi203 unchanged;

FIG. 21 is a curve diagram of piezoelectric properties where the proportions of PbTiO3 and PbZrOa are varied with those of Pb(Cd1/3Nb2/3)O3 and auxiliary La203 unchanged;

FIGS. 22 and 23 represent the piezoelectric properties of two samples of the invention containing auxiliary LanOa; FIG. 22 is a curve diagram of the relationship 4 of temperature and dielectric constant and FIG. `23 is a curved diagram of'the relationship of temperature and electro-mechanical coupling coetcient;

FIG. 24 is a curve diagram showing change with time in the resonance frequency after polarization as associated with two samples of thel invention only consisting ofthe basic-constituent and two other samples containing La203 asan auxiliary component;

FIG. 25 is a curve diagram showing change with time in the electro-mechanical coupling coei'icient as associated' with the four samples of FIG. 24;

FIG. 26 is a comparative curve diagram showing the temperature characteristics of the resonance frequency after polarization as associated with two samples of the invention respectively involving La2O3 alone and a mixture of La203 and Bi203 as auxiliary components and one sample of the prior art;

FIG. 27 is a curve diagram of piezoelectric properties where the proportions of Pb (Cd1/3'Nb2/3)O'3, PbTiOs and PbZrO3 are varied with that of auxiliary Th02 iixed;

FIG. 28 is a curve, diagram of piezoelectric properties where the proportions of PbTiO3 and PbZrO3 are varied with those of Pb (Cd1/3Nb2/3)O3 and auxiliary CeO2 unchanged;

FIGS. 29 and 30 indicate the piezoelectric properties` of two samples ofthe invention containing auxiliary ThO2; FIG. 29 is a curve diagram of the relationship of temperature and dielectric constant and FIG. 30 is a curve diagram of the relationship of temperature and electro-mechanical coupling coefficient;

FIG. 31 is a curve diagram showing change with time after polarization in the resonance frequency as associated with two samples of the invention consisting of the basic constituent and two other samples containing auxiliary CeOZ and T1102 respectively;

FIG. 32 is a curve diagram showing change with time in the electro-mechanical coupling coeflicient as associated with the four samples of FIG. 31; and

FIG. 33 is a comparative curve diagram showing the temperature characteristics of the resonance frequency after polarization as associated with two samples of the invention containing auxiliary Th02 and two samples of the prior art.

The oxide piezoelectric material of the present invention is newly prepared by solid phase reaction from a plurality of oxides having different valencies, and consists of a ternary oxide system obtained by, substituting part of PbTiO3-PbZrO3 with a novel component of Pb(Cd1/3Nb2/3)O3 which is of perovskite crystal structure. 'Ihe piezoelectric material of the invention may be expressed as y=34.0 to 55.5 mol ypercent z=16.0 to 53.5 mol percent There will now be described the aforementioned novel component of Pb(Cd1/3Nb2/3)O3. With respect to this material, literature (Soviet Physics Doklady, vol. 9, No. 9, pp. 751-752, 1965 by Venevtsev et al. of Soviet Union discloses that it mayebe synthesized. However, said report makes no reference to the electrical properties, crystal structure and otherV properties. The present inventors studies show that Pb (Cdl/3 -Nb2/3)O3 is of perovskite crystal structure wherein the lattice constant a indicates 4.11 A.

The aforementioned basic constituent of an oxide piezoelectric material can be easily prepared by the ordinary sintering techniques (as described below. Raw oxide, for example, PbO, TiO2,ZrO2, Nb205 and CdO are weighed outiexactly to the prescribed proportions and mixed in a ball mill or'the like.fThe raw materials'used in this case mayV consist of other substances such as hydrexides, carbonates and oxalates which, upon heating, are converted to oxides. The aforesaid mixture is presintered at a relatively low temperature, for example, 600 to 900 C. and further ground in a ball mill to form conditioned powders. To said powders is added a binder such as water, or polyvinyl alcohol. The mass is molded at a pressure of about 0.2 to 2 ton/cm.2 and sintered at a temperature of about 1100 to l270 C. Since part of the PbO is likely to be evaporated and scattered, said sintering is conducted in a sealed furnace, preferably maintaining a maximum temperature generally for about 0.5 to 3 hours. Polarization of an oxide piezoelectric material can be effected by a known method of, for example, fitting a pair of electrodes to its both sides and impressing a D.C. field of to 30 kv./ cm. thereon for about one hour in a silicone oil at a temperature of about 140 to 160 C. This process easily produces a piezeolectric material which has a different composition from the known product of a binary system of or that consisting of CdO or ZnO added to said system or a ternary system of Pb(Mg1/3'Nb2/3)O3=PPbTiO3PbZrO3 and displays better properties than any of the prior art.

It is for the following reason that Pb(Cd1/3Nb2/3)O3, PbTiO3 and PbZrO3 constituting the oxide piezoelectric material of the present invention have been chosen to assume the aforementioned proportions.

To begin with, if the proportion of Pb (Cd1/3Nb2/3)03 involved in the basic constituent exceeds 50.0%, then the electro-mechanical coupling coefficient Kp demanded of a piezoelectric material used in practical applications, for example, a pickup or microphone, will fall to below 43%. Again, if said proportion decreases to below 1.0%, then there will be presented difficulties in sintering a dense and mechanically strong piezoelectric material and the electro-mechanical coupling coefficient Kp will also be reduced to 43%, preventing such product from fully meeting industrial requirements. Referring next to PbTiO3, if its proportions rise above 55.5% or decrease to below 34.0%, then the resultant piezoelectric material will not have a large electro-mechanical coupling coefficient Kp nor be capable of preserving substantially unchanging properties regardless of temperature variation and over a long period of time, failing to be fully satisfactorily used in industrial application, for example, an oscillation element for generating supersonic waves. Last, where the proportion of PbZrO3 increases over 53.5% or falls to below 16.0% then there will result a piezoelectric material which does not have a large electro-mechanical coupling coeficient Kp and consequently is of little use in piezoelectric applications. Accordingly, the proportions of PbTiO3 and PbZrO3 forming the ternary basic constituent of the present piezoelectric material are selected from the hatched range of FIG. 1.

The aforementioned oxide piezoelctric material of the present invention assumes the so-called perovskite structure (as determined by X-ray diffraction) in which there are uniformly distributed PbO, TiO2, ZrO2, CdO and Nb205 in the form of solid solution. If expressed by the general formula ABO3, said piezoelectric material comprises divalent Pb represented by A and divalent Cd, pentavalent Nb and tetravalent Ti and Zr represented by B, namely, A and B are respectively formed of a combination of elements having different valencies. ln this respect, the piezoelectric material of the present invention is essentially different from that of the prior art which mainly assumes an oxygen-containing octahedron and whose composition is such that if expressed by the general formula ABO3, elements represented by B' are tetra-f valent when those of A' are divalent or elements represented by B are pentavalent when those of A are univalent, namely, A and B' respectively consist of a combination of elements having the same valency. p Y' As already described, the piezoelectric material of the present invention also includes the type consisting of the aforementioned ternary basic constituent assuming the form of a solid solution and an auxiliary component added thereto in a specified proportion such as M1102, Cl'zoa, COO, 1.13203, Bl203, Or C602.

Where the proportion of MnO2 added as an auxiliary component to said basic constituent exceeded 2% by weight, it was found that the mechanical quality factor QM of the resultant piezoelectric material was conversely reduced, leading to sufficiently great decrease in its specie resistivity to render the subsequent polarization unsatisfactory, and in consequence the conduction and short circuiting of unnecessary |parts during the impression of a D C. voltage, so that polarization ywas not fully carried out, making it impossible to improve the mechanical quality factor QM. `Also Where the proportion of MnO2 fell to -below 0.01%, the mechanical quality factor QM Was little improved, eventually failing to obtain a piezoelectric material having the desired excellent properties. Accordingly, addition of Mn02 is preferably made within the range of 0.01 to 2.0% by Weight. This auxiliary component of MnOZ also acts as a mineralizer to facilitate sintering. Ease of sintering leads to decrease in sintering temperature, thereby suppressing the evaporation of PrbO involved in the basic constitutent and eventually producing a dense piezoelectric material.

According to the present invention, addition of auxiliary NiO or CoO alone or in combination to said 4basic comstituent is always limited to the range of 0.1 to 2.5% by weight. Following is the reason. Where the proportion of NiO increases over 2.5% by weight, the QM of the resultant piezoelectric material is conversely reduced, leading to sufficiently -great decrease in its specific resistivity to render the subsequent polarization unsatisfactory and in consequence the conduction and short circuiti-ng of unnecessary parts during the impression of a D.C. voltage, so that polarization is not fully carried out, making it impossible to improve QM. Also Where addition of NiO falls to below 0.1% by weight, QM is not much elevated. NiO, CoO or a mixture thereof also acts as a mineralizer to facilitate sintering. Ease of sintering leads to decrease in sintering temperature, thereby not only supressing the evaporation of P-bO involved in the basic constituent and producing a dense piezoelectric material but also elevating Kp to 45 to 70% and QM excellent to 250 to 2000. Accordingly, this piezoelectric material fully meets the requirements of practical applications, for example, a transducer like a pickup, microphone, or oscillator or an ignition element.

Furthermore, an oxide piezoelectric material containing NiO or COO according to the present invention varies very little in its piezoelectric properties with respect to temperature change, for example, from 50 to 200 C. and during a long period of time after polarization, namely, the product always maintains good stable properties and exhibits a prescribed performance. The fact that the present piezoelectric material displays such good stable properties offers the followin-g advantages When it is put to practical use. For example, Where a filter or resonator is prepared from such oxide piezoelectric materials, it presents little variation in frequency over a temperature range of 40 to 80 C. due to its good temperature characteristics and exhibits a prescribed performance. Since it presents little change with time in its properties as shown in FIG. 18, it is available for use over a long period of time. Variation in frequency about 10 years after its preparation only amounts to less than 0.15%. Such a prominent feature has been unrealizable with any piezoelectric material of the prior art.

When La203, Bi203 or a mixture thereof is added to said ternary basic constituent of 

